1. Field of the Invention
This invention relates to apparatus for mounting roller cutters onto a cutterhead from the rear of the cutterhead, and in particular to cutter mounting apparatus which carries the thrust loads imposed on the roller cutters in shear and/or compression and directly transmits such loads to the cutterhead frame.
2. Description of the Prior Art
U.S. Pat. No. 3,237,990, granted Mar. 1, 1966 to Richard J. Robbins and Douglas F. Winberg, and U.S. Pat. No. 3,191,699, granted June 29, 1965, also to Richard J. Robbins and Douglas F. Winberg, both present a good description of how a disc type roller cutter works. U.S. Pat. No. 3,237,990 discloses a typical pattern of disc cutters on a large diameter cutterhead. U.S. Pat. No. 3,191,699 discloses a particular mount for a disc cutter.
U.S. Pat. No. 3,612,196, granted Oct. 12, 1971, to Robert L. Dixon, discloses a second common type of roller cutter and another type of cutter mount.
The cutter mounts disclosed by U.S. Pat. Nos. 3,191,699 and 3,612,196 are both front access or front loaded type mounts. That is, the cutters must be replaced from the front side of the cutterhead. In order to replace a cutter the drilling machine must be backed up to provide a space between the tunnel face and the front of the cutterhead. A workman must then enter the space in order to change the cutter.
It is known in the prior art to mount roller type cutters from behind the cutterhead (i.e. back loading) so that the machine need not be backed up and the workmen need not be subject to the dangers inherent to having to work in the space between the cutterhead and the tunnel face. However, the known rear access or back loaded cutter mounts are constructed essentially like the cutter mount disclosed by the aforementioned U.S. Pat. No. 3,191,699, except that the support frame or block is built into the cutterhead and the retaining cap is directed rearwardly. An example of such a rear access cutter mount is disclosed by U.S. Pat. No. 3,444,939, granted May 20, 1969 to Karl G. Bechem. A disadvantage of this type of mount is that the thrust loads which are imposed on the cutters are carried by bolts in tension and their failure rate is relatively high.